Breath figures under electrowetting: electrically controlled evolution of drop condensation patterns

We show that electrowetting (EW) with structured electrodes significantly modifies the distribution of drops condensing onto flat hydrophobic surfaces by aligning the drops and by enhancing coalescence. Numerical calculations demonstrate that drop alignment and coalescence are governed by the drop size-dependent electrostatic energy landscape that is imposed by the electrode pattern and the applied voltage. Such EW-controlled migration and coalescence of condensate drops significantly alter the statistical characteristics of the ensemble of droplets. The evolution of the drop size distribution displays self-similar characteristics that significantly deviate from classical breath figures on homogeneous surfaces once the electrically-induced coalescence cascades set in beyond a certain critical drop size. The resulting reduced surface coverage, coupled with earlier drop shedding under EW, enhances the net heat transfer.Comment: 5 pages, 5 figure

Pola Kerontokan Buah Tiga Kultivar Mangga

Information on the pattern of fruit drop of mango is required to determine the appropriate method and time in reducing fruit drop. By this methodf, fruit retention or number of harvested fruit of mango can be increased.The aim of this research was to determine the pattern of fruit drop of Gadung 21, Manalagi 69 and Golek 3 I . The results of this researchs howedt hat the pattern of fruit drop of Gadung2 1, Golek 31 and Manalagi 69 was similar. All cultivars I showed that there was one peak (the highest number of fruit drop) in fruit drop. It occurred at 6 days after anthesis (DAA). After 24 DAA, the number offruit drop was constant, namely near to zero. It occurred until harvest

Patterns Formation in Drying Drops of Blood

The drying of a drop of human blood exhibits coupled physical mechanisms, such as Marangoni flow, evaporation and wettability. The final stage of a whole blood drop evaporation reveals regular patterns with a good reproducibility for a healthy person. Other experiments on anaemic and hyperlipidemic people were performed, and different patterns were revealed. The flow motion inside the blood drop is observed and analyzed with the use of a digital camera: the influence of the red blood cells (RBCs) motion is revealed at the drop periphery as well as its consequences on the final stage of drying. The mechanisms which lead to the final pattern of the dried blood drops are presented and explained on the basis of fluid mechanics in conjunction with the principles of haematology. The blood drop evaporation process is evidenced to be driven only by Marangoni flow. The same axisymetric pattern formation is observed, and can be forecast for different blood drop diameters. The evaporation mass flux can be predicted with a good agreement, assuming only the knowledge of the colloids mass concentration.Comment: 1 page + conference APS 2011 (1 movie for the gallery + 1 movie for ArXiv

Tailoring surface interactions, contact angles, drop topologies and self-assembly using laser irradiation

UV laser irradiation (lambda = 193 nm), below and above damage thresholds, is used to both alter and pattern the surface properties of borosilicate slides to tune and control the contact angle of a water drop over the surface. Large variation exceeding 25 deg using laser processing alone, spanning across both sides of the original contact angle of the surface, is reported. An asymmetric contact angle distribution, giving rise to an analogous ellipsoidal-like drop caplet, is shown to improve convective self-assembly of silica nanoparticles into straighter microwires over a spherical caplet.Comment: Submitted to Beilstein Publishing 27 August 201

Faraday instability on a sphere: numerical simulation

We consider a spherical variant of the Faraday problem, in which a spherical drop is subjected to a time-periodic body force, as well as surface tension. We use a full three-dimensional parallel front-tracking code to calculate the interface motion of the parametrically forced oscillating viscous drop, as well as the velocity field inside and outside the drop. Forcing frequencies are chosen so as to excite spherical harmonic wavenumbers ranging from 1 to 6. We excite gravity waves for wavenumbers 1 and 2 and observe translational and oblate-prolate oscillation, respectively. For wavenumbers 3 to 6, we excite capillary waves and observe patterns analogous to the Platonic solids. For low viscosity, both subharmonic and harmonic responses are accessible. The patterns arising in each case are interpreted in the context of the theory of pattern formation with spherical symmetry

Solidification of liquid metal drops during impact

Hot liquid metal drops impacting onto a cold substrate solidify during their subsequent spreading. Here we experimentally study the influence of solidification on the outcome of an impact event. Liquid tin drops are impacted onto sapphire substrates of varying temperature. The impact is visualised both from the side and from below, which provides a unique view on the solidification process. During spreading an intriguing pattern of radial ligaments rapidly solidifies from the centre of the drop. This pattern determines the late-time morphology of the splat. A quantitative analysis of the drop spreading and ligament formation is supported by scaling arguments. Finally, a phase diagram for drop bouncing, deposition and splashing as a function of substrate temperature and impact velocity is provided

Drop out from Wanganui Regional Community Polytechnic, 1992-1993 : a thesis presented in partial fulfilment of the requirements for the degree of Master of Educational Administration, Massey University

In New Zealand recent changes in legislation have increased both the autonomy and accountability of the tertiary education sector. As a consequence, polytechnics have become painfully aware of the cost of student drop out from programmes both to their credibility as quality education providers and to their coffers. The case study of student drop out from Wanganui Regional Community Polytechnic (WRCP) was undertaken in response to administrators' concerns that, as a small, recently established polytechnic, costs associated with the loss of students might threaten its economic viability. WRCP administrators feared an increase in the rate of drop out as changes to the funding of tertiary study created increased financial pressures for students. The case Study employed a range of techniques, including a survey of archived information and student questionnaires, augmented by the perceptions gained from informal discussions with staff to ascertain the extent and nature of drop out. Analysis of data collected over a two year period (1992-1993) at WRCP revealed a pattern of drop out in terms of student characteristics, style and timing of withdrawal. Overall it showed that there was little to discriminate between the characteristics of leavers and those who persisted on a course. The two main theoretical conceptualisations of drop out, the 'integration' and 'investment' theories, were found to share the assumption that drop out is the consequence of 'cost/benefit' analysis. However, despite increased fees and reduced allowances for many students, few cited financial reasons for withdrawal. An analysis of students' self-reported reasons for leaving indicated that finances are but one of many factors which affect a students determination of the costs and benefits of continued attendance. Many reasons given were outside the control of the Polytechnic. However, three Polytechnic academic schools were consistent in their reporting of high drop out numbers, suggesting the need for further research into programme related reasons for withdrawal in these areas. These findings were consistent with recent models, which portray drop out as a complex process influenced by a multitude of factors, including student background and characteristics on entry, environmental changes and institutional factors. From those findings some strategies to enhance the 'fit' of students and hence improve their retention are suggested. Continued monitoring and further research of a more phenomenological nature are recommended in order to gain a greater understanding of student drop out

Optimal LQG Control Across a Packet-Dropping Link

We examine optimal Linear Quadratic Gaussian control for a system in which communication between the sensor (output of the plant) and the controller occurs across a packet-dropping link. We extend the familiar LQG separation principle to this problem that allows us to solve this problem using a standard LQR state-feedback design, along with an optimal algorithm for propagating and using the information across the unreliable link. We present one such optimal algorithm, which consists of a Kalman Filter at the sensor side of the link, and a switched linear filter at the controller side. Our design does not assume any statistical model of the packet drop events, and is thus optimal for an arbitrary packet drop pattern. Further, the solution is appealing from a practical point of view because it can be implemented as a small modification of an existing LQG control design